Welding stainless to mild steel?

[Memfuzz]

I recently saw a work table made from mild steel 1/4 2x2 angle for the frame and legs. The top was 3/16 stainless that was tacked in several places underneath. I'd like to do this, but have never worked with stainless. I'll be using a MM210. Any tips on wire, gas, etc? Thanks in advance, Brad.

[Dan]

For what you are wanting to do, there is really no need to weld the top to the framework with stainless. I work with a lot of stainless and if you haven t priced this sheet yet you may change your mind about this once you see how much the sheet costs. As an example most of my sheet metal work is with 16ga 304. And on average a 4' x 8' sheet of this 16 ga costs my work $150. I wouldn t be suprised if a sheet of 3/16 wasn t $500 +.

[Memfuzz]

I was wrong, it's 3/8 thick. I realize it's going to be expensive, but the guy I'm building them for specs it to be stainless. It's going to be an inpection table, any other material can introduce contamination. It also has to be that thick, so the surface won't warp. The one he has now cost him about $1500. He wants me to see if I can beat the price. I'd like to make some to pay my hobby fund back for the Miller, and think about getting a TIG machine and learning that process, along with upgrading to a better bandsaw. Hate my import 4X6 model.

[Dan]

Originally posted by Memfuzz
I was wrong, it's 3/8 thick. I realize it's going to be expensive, but the guy I'm building them for specs it to be stainless. It's going to be an inpection table, any other material can introduce contamination. It also has to be that thick, so the surface won't warp. The one he has now cost him about $1500. He wants me to see if I can beat the price. I'd like to make some to pay my hobby fund back for the Miller, and think about getting a TIG machine and learning that process, along with upgrading to a better bandsaw. Hate my import 4X6 model.

Sorry, thought you were making a table for yourself. Anyway, since the welds are on the underside, steel wire should be ok. However you re probably wanting to do this with stainless, and to the best of my knowledge 309 stainless filler is used to joining mild steel and 304 stainless steel.

[Roger]

If you could use countersunk machine screws then no warping.

[Memfuzz]

Originally posted by Roger
If you could use countersunk machine screws then no warping.

Yeah, I had thought about that, but haven't had the chance to ask if that would be acceptable. Thanks for all the info so far guys!

[Mike Sherman]

Welding an austenitic stainless steel to carbon steel is best done with a stainless filler with a total alloy content high enough to prevent the formation of martensite in the weld after dilution. You run the risk of cracking if you don't. Standard practice when welding carbon steel to stainless such as 304 is butter a pass of E309 onto the carbon steel and then weld the two pieces together. If it is very thin and this isn't practical and the weld is not under restraint, weld it with E309 in one pass. By the way, I would have to pay $709.00 for a 4' x 8' x .375 plate of 304, delivered.

[Roger]

Weld on stainless steel tabs then bolt or weld to that.

With stainless steel bolts I always use anti-seize compound when allowed.

[Guest]

Stainless doesn't quite weld like mild steel, in that the color is different, from a black to a golden brown, using A10-25 tri mix gas. Which is a mixture of Helium, argon and Co2. It takes a while to get used to. My certification in 304 SS to A36 steel was using 308 wire, both in GMAW and GTAW. I will say here, though, I have a high regard for what Mike Sherman says, and when he says 309...that's good enough for me!

Keep us informed, it sounds interesting!